a. Field of the Invention
The present invention pertains generally to rendering digital images and specifically to high speed rendering vector and raster images using caching.
b. Description of the Background
Maps and other large graphical databases are difficult to display and manipulate on smaller computing devices. For example, hand held computers have small displays but also slow central processing units and limited memory. For these devices to be useful to display and manipulate image databases, the speed and memory limitations must be overcome. Other computing devices have similar memory and computational power limitations and can also benefit from enhanced performance.
Map data comes in two general forms: raster and vector data. Raster data may be bitmap images, such as aerial photographs and topological maps. Some map data may be in the form of vector data. For example, political boundaries or the routes of the interstate highway system may be in vector form. The generation of images may comprise both raster and vector data.
Databases that contain large images are often terabytes in size whereas the computing devices, such as hand held computers, may have only megabytes of storage space. Only a small portion of the database may be stored locally and used at any one time. In many cases, when a user pans or zooms the image, they may have to wait for a new portion of the database to be loaded and displayed on the screen. Sometimes, the ‘lag time’ for the new information to load is noticeable and frustrating for the user.
It would therefore be advantageous to provide a system and method for caching and rendering image databases that is fast and uses memory efficiently. It would further be advantageous if the system and method used the displaying computer's computational power efficiently.